# 毕业论文中英文文献翻译 工程机械运用维护毕业论文.doc

毕业论文中英文文献翻译 工程机械运用维护毕业论文 附 录 Semi-automatic control system for hydraulic shovel Hirokazu Araya, Masayuki Kagoshima Mechanical Engineering Research Laboratory, Kobe Steel, Ltd., Nishi-ku, Kobe Hyogo 651 2271, Japan Accepted 27 June 2000 Abstract A semi-automatic control system for a hydraulic shovel has been developed. Using this system, unskilled operators can operate a hydraulic shovel easily and accurately. A mathematical control model of a hydraulic shovel with a controller was constructed and a control algorithm was developed by simulation. This algorithm was applied to a hydraulic shovel and its effectiveness was evaluated. High control accuracy and high-stability performance were achieved by feedback plus feedforward control, nonlinear compensation, state feedback and gain scheduling according to the attitude. q2001 Elsevier Science B.V. All rights reserved. Keywords: Construction machinery; Hydraulic shovel; Feedforward; State feedback; Operation 1.Introduction A hydraulic shovel is a construction machinery that can be regarded as a large articulated robot. Digging and loading operations using this machine require a high level of skill, and cause considerable fatigue even in skilled operators. On the other hand, operators grow older, and the number of skilled operators has thus decreased. The situation calls for hydraulic shovels, which can be operated easily by any personw15x. The reasons why hydraulic shovel requires a high level of skill are as follows. More than two levers must be operated simultaneously and adjusted well in such operations. The direction of lever operations is different from that of a shovels attachment movement. For example, in level crowding by a hydraulic shovel, we must operate three levers Žarm, boom, bucket. simultaneously to move the top of a bucket along a level surfaceŽFig. 1 In this case, the lever operation indicates the direction of the actuator, but this direction differs from the working direction. If an operator use only one lever and other freedoms are operated automatically, the operation becomes very easily. We call this system a semi-automatic control system. When we develop this semi-automatic control system, these two technical problems must be solved. 1. We must use ordinary control valves for automatic control. 2. We must compensate dynamic characteristics of a hydraulic shovel to improve the precision of control. We have developed a control algorithm to solve these technical problems and confirm the effect of this control algorithm by experiments with actual hydraulic shovels. Using this control algorithm, we have completed a semi-automatic control system for hydraulic shovels. We then report these items. 2.Hydraulic shovel model To study control algorithms, we have to analyze numerical models of a hydraulic shovel. The hydraulic shovel, whose boom, arm, and bucket joints are hydraulically driven, is modeled as shown in Fig.2. The details of the model are described in the following. 2.1. Dynamic model [6] Supposing that each attachment is a solid body, from Lagranges equations of motion, the following expressions are obtained: where, g is the joint angle, i is the supply torque, i is the attachment length, li is the distance between lgi the fulcrum and the center of gravity, mi is the mass of the attachment, Ii is the moment of inertia around the center of gravity (subscripts i=13, mean boom, arm, and bucket, respectively) 2.2. Hydraulic model Each joint is driven by a hydraulic cylinder whose flow is controlled by a spool valve, as shown in Fig.3. We can assume the following: 1. The open area of a valve is proportional to the spool displacement. 2. There is no oil leak. 3. No pressure drop occurs when oil flows through piping. 4. The effective sectional area of the cylinder is the same on both the head and the rod sides. In this problem, for each joint, we have the following equation from the pressure flow characteristics of the cylinder: when, where, Ai=seffective cross-sectional area of cylinder; hi=cylinder length; Xi= spool displacement; Psi= supply pressure; P1i=cylinder head-side pressure; P2icylinder rod-side pressure; Vi=oil volume in the cylinder and piping; Bi=pool width; =oil density; K=bulk modulus of oil; and c=flow coefficient. 2.3. Link relations In the model shown in Fig. 1, the relation between the cylinder length change rate and the attachment rotational angular velocity is given as follows:(1). Boom arm 1、 Bucket When 2.4. Torque relations From the link relations of Section 2.3, the supply torque i is given as follows, taking cylinder friction into consideration: Where, Cci the viscous friction coefficient and Fi kinetic frictional force of a cylinder. 2.5. Response characteristics of the spool Spool action has a great effect on control characteristics. Thus, we are assuming that the spool has the following first-order lag against the reference input. Where, is the reference input of spool displacement and a time constant. 3. Angle control system As shown in Fig. 4, the angle is basically controlled to follow the reference angle by position feedback. In order to obtain more accurate control, nonlinear compensation and state feedback are added to the position feedback. We will discuss details of these algorithms as follows. 3.1. Nonlinear compensation In the ordinary automatic control systems, new control devices such as servo valves are used. In our semi-automatic system, in order to realize the coexistence of manual and automatic operations, we must use the main control valves, which are used in manual operation. In these valves, the relation between spool displacement and open area is nonlinear. Then, in automatic operation, using this relation, the spool displacement is inversely calculated from the required open area, and the nonlinearity is compensated(Fig.5) 3.2. State feedback Based on the model discussed in Section 2, if the dynamic characteristics for boom angle control are linearized in the vicinity of a certain standard condition (spool displacement X 10, cylinder differential pressure P 110 , and boom angle 10)., the closed-loop ransfer function can be expressed by where, Kpposition feedback gain; and This system has a comparatively small coefficient a1 , so the response is oscillatory. For instance, if in our large SK-16 hydraulic shovel, X 10 is 0, the 10 coefficients are given as , a 0 =2.7 10 ,a 1 =6.0 10 ,a 2 =1.2 10 . Addingthe acceleration feedback of gain Ka , to this (the upper loop in Fig. 4.), the closed loop transfer function is given as Adding this factor, the coefficient of S becomes larger, thus, the system becomes stable. In this way, acceleration feedback is effective in improving the response characteristics. However, it is generally difficult to detect acceleration accurately. To overcome this difficulty, cylinder force feedback was applied instead of acceleration feedback(the lower loop in Fig. 40 In this case, cylinder force is calculated from detected cylinder pressure and filtered in its lower-frequency portion [7,8]. This is called pressure feedback. 4. Servo control system When one joint is manually operated and another joint is controlled automatically to follow the manual operation, a servo control system must be required. For example, as shown in Fig. 6, in the level crowding control, the boom is controlled to keep the arm end height Z(calculated from 1 and 2 ).to reference Zr. In order to obtain more accurate control, the following control actions are introduced. 4.1. Feedforward control Calculating Z from Fig. 1, we obtain Differentiating both sides of Eq.(8). with respect to time, we have the following relation, The first term of the right-hand side can be taken as the expression(feedback portion).to convert to 1 , and the second term of the right-hand side is the 1 expression(feedforward portion).to calculate how much 1 should be changed when 2 is changed 1 2= manually. Actually, 1is determined using the difference value of △ 2 . To optimize the feedforward rate, feedforward gain Kff tunned. There may be a method to detect and use the arm operating-lever condition(i.e. Angle).instead of arm angular velocity, since the arm is driven at an angular velocity nearly proportional to this lever condition. 4.2. Adapti6e gain scheduling according to the attitude In articulated machines like hydraulic shovels, dynamic characteristics are greatly susceptible to the attitude. Therefore, it is difficult to control the machine stably at all attitudes with constant gain. To solve this problem, the adaptive gain scheduling according to the attitude is multiplied in the feedback loop(Fig. 6) As shown in Fig. 7, the adaptive gain (KZ or K ).is characterized as a function of two variables2 , and Z. 2 means how the arm is extended, and Z means the height of the bucket. 5. Simulation results The level crowding control was simulated by applying the control algorithm described in Section 4 to the hydraulic shovel model discussed in Section 2. (In the simulation, our large SK-16 hydraulic shovel was employed.). Fig. 8 shows one of the results. Five seconds after the control started, load disturbance was applied stepwise. Fig. 9 shows the use of feedforward control can reduce control error. 6. Semi-automatic control system As illustrated in Fig. 10, the control system consists of a controller, sensors, manmachine interface, and hydraulic control system. The controller is based on a 16-bit microcomputer which receives angle input signals of the boom, arm, and bucket from the sensor; determines the condition of each control lever; selects control modes and calculates actuating variables; and outputs the results from the amplifier as electrical signals. The hydraulic control system generates hydraulic pressure proportional to the electrical signals from the electromagnetic proportional-reducing valve, positions the spool of the main control valve, and controls the flow rate to the hydraulic cylinder. In order to realize high-speed, high-accuracy control, a numeric data processor is employed for the controller, and a high-resolution magnetic encoder is used for the sensor. In addition to these, a pressure transducer is installed in each cylinder to achieve pressure feedback. The measured data are stored up to the memory, and can be taken out from the communication port. 6.2. Control functions This control system has three control modes, which are automatically switched in accordance with lever operation and selector switches. These functions are the following (1).Level crowding mode: during the manual arm pushing operation with the level crowding switch, the system automatically controls the boom and holds the arm end movement level. In this case, the reference position is the height of the arm end from the ground when the arm lever began to be operated. Operation of the boom lever can interrupt automatic control temporarily, because priority is given to manual operation. (2)Horizontal bucket lifting mode: during the manual boom raising operation with the horizontal bucket lifting switch, the system automatically controls the bucket. Keeping the bucket angle equal to that at the beginning of operation prevents material spillage from the bucket. (3)Manual operation mode: when neither the level crowding switch nor the horizontal bucket lifting switch are selected, the boom, arm, and bucket are controlled by manual operation only. The program realizing these functions is primarily written in C language, and has well-structured module to improve maintainability. 7. Results and analysis of field test We put the field test with the system. We confirmed that the system worked correctly and the effects of the control algorithm described in Chaps. 3 and 4 were ascertained as follows. 7.1. Automatic control tests of indi8idual attachments For each attachment of the boom, arm, and bucket, the reference angle was changed 58 stepwise from the initial value, and the responses were measured; thus, the effects of the control algorithm described in Chap. 3 were ascertained. 7.1.1. Effect of nonlinear compensation Fig. 11 shows the test results of boom lowering. Because dead zones exist in the electro-hydraulic systems, steady-state error remains when simple position feedback without compensation is applied (OFF in the figure) Addition of nonlinear compensation (ON in the figure).can reduce this error. 7.1.2. Effect of state feedback control For the arm and bucket, stable response can be obtained by position feedback only, but adding acceleration or pressure feedback can improve fast-response capability. As regards the boom, with only the position feedback, the response becomes oscillatory. Adding acceleration or pressure feedback made the response stable without impairing fast-response capability. As an example, Fig. 12 shows the test results when pressure feedback compensation was applied during boom lowering. 7.2. Le9el crowding control test Control tests were conducted under various control and operating conditions to observe the control characteristics, and at the same time to determine theoptimal control parameters (such as the control gainsshown in Fig. 6) 7.2.1. Effects of feedforward control In the case of position feedback only, increasing gain Kp to decrease error ∆Z causes oscillation due p to the time delay in the system, as shown by AOFFB in Fig. 13. That is, Kp cannot be increased. Apply- p ing the feedforward of the arm lever value described in Section 4.1 can decrease error without increasing K as shown by AONB in the figure. 7.2.2. Effects of compensation in attitude Level crowding is apt to become oscillatory at the raised position or when crowding is almost completed. This oscillation can be prevented by changing gain Kp according to the attitude, as has been p iscussed in Section 4.2. The effect is shown in Fig.14. This shows the result when the level crowding was done at around 2 m above ground. Compared to the case without the compensation, denoted by OFF in the figure, the ON case with the compensation provides stable response. 7.2.3. Effects of control inter9al The effects of control interval on control performance were investigated. The results are: 1. when the control interval is set to more than 100 ms, oscillation becomes greater at attitudes with large moments of inertia; and 2. when the control interval is less than 50 ms, control performance cannot be improved so much. Consequently, taking calculation accuracy into account, the control interval of 50 ms was selected for this control system. 7.2.4. Effects of load A shovel with this control system carried out actual digging to investigate the effects of loading. No significant difference was found in control accuracy from that at no load 8. Conclusions This paper has shown that combining state feedback and feedforward c